Mesa Verde in SW Colorado is a "must see" place. It was inhabited by Anasazi Indians around 1200 AD to 1280 AD after which they disappeared with no traces, and we still do not know today what became of them (theories expounded by Stephen Lekson in "A History of the Ancient Southwest" are promising but are not accepted by a consensus of archaeologists yet). They made communal dwellings in cliff niches that had a strong defensive position -- what were they afraid of? The ruins are very moving and compelling. Do some on-line research about the site and about how much time it takes. Take water to drink.

The Durango-Silverton railroad is well worth riding in Durango. Take the train from Durango up to Silverton, but take an alternative back from Silverton to Durango, like a bus. The train ride takes a lot of time, and you will have seen all the same scenery on the way up to Silverton. Beautiful mountain views.

Meteor crater about 40 miles east of Flagstaff, Arizona, is worth a look if it is on the way. Grand Canyon is north of Flagstaff, worth seeing. The north rim is thought to be the best by friends of mine who have been to the Grand Canyon many times.